A wood utility pole, formed from the trunk of a tree, is typically used for supporting high voltage (HV) conductors (e.g., twisted wire strands) in a power distribution system. Since the poles are formed from trees, the pole diameters vary from pole to pole. For example, the pole may have a diameter at the top of the pole of five inches, and four feet down from the top of the pole it may be ten inches. Another pole may have a diameter at the top of ten inches, and four feet down from the top it may have a diameter of fourteen inches.
Each pole has secured to it one or more horizontal crossarms that support ceramic insulators which, in turn, support the HV conductors. Two crossarms are popular for their added strength and reliability. The crossarms are affixed to the pole using either bolts, a brace, a bracket, or other means. A conductor is typically affixed over the top of each insulator via a metal tie wire, a bracket, or other means.
FIG. 1 is a side view of a top portion of a wooden pole 10, looking into the ends of two horizontal crossarms 12 and 14. FIG. 2 is a top down view of the pole 10 of FIG. 1 showing four sets of insulators supporting four conductors. The crossarms 12 and 14 are typically wood, such as 6 feet×3.5 inches×4.5 inches, depending on the support strength needed for the conductors. Material other than wood is also used for crossarms.
Ceramic insulators 16 and 18 are affixed to the crossarms 12 and 14 by bolts 20. A conductor 22 (typically twisted wire strands) seats in a groove in the insulators 16/18 or in some other securing feature, as previously described.
The crossarms 12/14 in FIG. 2 are shown supporting additional sets of insulators supporting additional conductors for 3-phase voltages. Alternatively, additional crossarms attached at different heights on the pole 10 may support the additional sets of insulators and the conductors for 3-phase voltages. The invention is applicable to all of the sets of insulators.
Since the diameter of the pole 10 is variable, the separation of the insulators 16/18 is unknown prior to the pole 10 being assembled. Typical separations are 5-16 inches.
Insulator covers, which are used in conjunction with extension arms that cover a length of the conductors, are frequently used for the protection of wildlife and preventing outages, permanent or momentary, due to shorts by trees, wildlife, debris, etc. The insulator/conductor covers are typically required to be 72 inches in length according to the Suggested Practices Guide developed by the Avian Power Line Interaction Committee (APLIC). Insulator/conductor covers measure 36 inches in one direction from the center of the insulator and 36 inches in the other direction. To obtain this 72 inch coverage, manufacturers have been designing these covers in three separate parts: the insulator cover, one extension arm connectable to one side of the insulator cover, and a second extension arm connectable to the other side of the insulator cover.
For covering the insulators 16 and 18 in FIG. 1 along with the conductor 22 between the insulators, such conventional covers would not work. This is because the distance between the insulators 16/18 varies from pole to pole, and an extension arm would be too long to fit between the insulators 16/18 and/or the extension arm would not precisely fit between the insulator covers. Additionally, the conductor 22 sags on one side of each insulator 16/18 due to the weight of the conductor 22 between poles, but the conductor 22 between the insulators 16/18 does not sag. The conventional extension arms could not accommodate the asymmetrical and variable conductor sag.
A one piece double insulator cover, with a fixed conductor cover between them, will not work or fit correctly around the two insulators 16/18 since their separation is unknown until the pole is assembled. A wide variety of double insulator covers would have to be available to the lineman, while in the field, in different sizes or lengths to accommodate all the possible separations of the insulators.
What is needed is a practical cover system for use with a pair of insulators supporting a conductor, where the separation between the insulators is variable.